Purified hydrogen peroxide gas generation methods and devices

ABSTRACT

The present disclosure provides for and includes improved devices and methods for the production of Purified Hydrogen Peroxide Gas (PHPG) that is substantially non-hydrated and substantially free of ozone.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/308,771, filed Nov. 3, 2016, which is a national stage application ofInternational Application No. PCT/US2015/029276 filed May 5, 2015, whichclaims priority to U.S. Provisional Application No. 61/988,535, filedMay 5, 2014, each of which is hereby incorporated by reference in theirentireties.

FIELD

The present disclosure relates generally to improved methods and devicesfor the production of purified hydrogen peroxide gas (PHPG). Morespecifically, this disclosure relates to improved air permeablesurfaces, catalytic surfaces and methods for increased production ofPHPG.

BACKGROUND

Pathogenic microbes, molds, mildew, spores, and organic and inorganicpollutants are commonly found in the environment. Microbial control anddisinfection in environmental spaces is desirable to improve health.Numerous ways have been used in the past in an attempt to purify air anddisinfect surfaces. For example, it is already known that ReactiveOxygen Species (ROS) produced by, e.g., photocatalytic oxidation processcan oxidize organic pollutants and kill microorganisms. Moreparticularly, hydroxyl radical, hydroperoxyl radicals, chlorine andozone, end products of the photocatalytic reaction, have been known tobe capable of oxidizing organic compounds and killing microorganisms.However, there are limitations to the known methods and devices, notonly due to efficacy limitation but also due to safety issues.

ROS is the term used to describe the highly activated air that resultsfrom exposure of ambient humid air to ultraviolet light. Light in theultraviolet range emits photons at a frequency that when absorbed hassufficient energy to break chemical bonds. UV light at wavelengths of250-255 nm is routinely used as a biocide. Light below about 181 nm, upto 182-187 nm is competitive with corona discharge in its ability toproduce ozone. Ozonation and UV radiation are both being used fordisinfection in community water systems. Ozone is currently being usedto treat industrial wastewater and cooling towers.

Hydrogen peroxide is generally known to have antimicrobial propertiesand has been used in aqueous solution for disinfection and microbialcontrol. Attempts to use hydrogen peroxide in the gas phase however,have previously been hampered by technical hurdles to the production ofPurified Hydrogen Peroxide Gas (PHPG). Vaporized aqueous solutions ofhydrogen peroxide produce an aerosol of microdroplets composed ofaqueous hydrogen peroxide solution. Various processes for “drying”vaporized hydrogen peroxide (VHP) solutions produce, at best, a hydratedform of hydrogen peroxide. These hydrated hydrogen peroxide moleculesare surrounded by water molecules bonded by electrostatic attraction andLondon Forces. Thus, the ability of the hydrogen peroxide molecules todirectly interact with the environment by electrostatic means is greatlyattenuated by the bonded molecular water, which effectively alters thefundamental electrostatic configuration of the encapsulated hydrogenperoxide molecule. Further, the lowest concentration of vaporizedhydrogen peroxide that can be achieved is generally well above the 1.0ppm Occupational Safety and Health Administration (OSHA) workplacesafety limit, making these processes unsuitable for use in occupiedareas.

Photocatalysts that have been demonstrated for the destruction oforganic pollutants in fluid include but are not limited to TiO₂, ZnO,SnO₂, WO₃, CdS, ZrO₂, SB₂O₄, and Fe₂O₃. Titanium dioxide is chemicallystable, has a suitable bandgap for UV/Visible photoactivation, and isrelatively inexpensive. Therefore, photocatalytic chemistry of titaniumdioxide has been extensively studied over the last thirty years forremoval of organic and inorganic compounds from contaminated air andwater.

Because photocatalysts can generate hydroxyl radicals from adsorbedwater when activated by ultraviolet light of sufficient energy, theyshow promise for use in the production of PHPG for release into theenvironment when applied in the gas phase. Existing applications ofphotocatalysis, however, have focused on the generation of a plasmacontaining many different reactive chemical species. Further, themajority of the chemical species in the photocatalytic plasma arereactive with hydrogen peroxide, and inhibit the production of hydrogenperoxide gas by means of reactions that destroy hydrogen peroxide. Also,any organic gases that are introduced into the plasma inhibit hydrogenperoxide production both by direct reaction with hydrogen peroxide andby the reaction of their oxidized products with hydrogen peroxide.

The photocatalytic reactor itself also limits the production of PHPG forrelease into the environment. Because hydrogen peroxide has greaterchemical potential than oxygen to be reduced as a sacrificial oxidant,it is preferentially reduced as it moves downstream in photocatalyticreactors as rapidly as it is produced by the oxidation of water.

TABLE 1 Oxidation/Reduction Half Reactions Standard ReductionPhoto-Activation of Catalyst Potential (eV) hv ⇄ h⁺ + e⁻ (on TiO₂catalyst) ≤−3.2 hv ⇄ h⁺ + e⁻ (on TiO₂ catalyst with co-catalyst) ≤−2.85Loss of Free Electrons Due to Electron-Hole Recombination h⁺ + e⁻ ⇄ heat(on TiO₂ catalyst) ≥3.2 h⁺ + e⁻ ⇄ heat (on TiO₂ catalyst withco-catalyst) ≥2.85 Formation of Hydroxyl Radicals (only if water isadsorbed on active sites on catalyst, preventing Electron-HoleRecombination) h⁺ + H₂O ⇄ OH* + H⁺ 2.85 Thermodynamically Favored lossof Hydroxyl Radicals by Free Electron Reduction in a Concentrated PlasmaReactor, but Avoided in a PHPG Reactor OH* + e⁻ + H⁺ ⇄ H₂O 2.02Combination of Hydroxyl Radicals to Form Hydrogen Peroxide is notThermodynamically Favored Compared to Free Electron Reduction in aPlasma Reactor, but is Promoted by a PHPG Reactor by Creating a DiluteHydroxyl Radical Field Separated from Free Electrons 2OH* ⇄ H₂O₂ 1.77Spontaneous Reactions That would Destroy any Hydrogen Peroxide inConcentrated Plasma Reactors, but which are Avoided by a PHPG Reactor byCreating a Dilute Hydroxyl Radical Field Separated from Free Electronsand Light 2OH* + H₂O₂ ⇄ 2H₂O + O₂ 2.805 H₂O₂ + 2H⁺ + 2e⁻ ⇄ 2H₂O 1.78H₂O₂ + hv ⇄ 2OH* (by Photolysis) 1.77 e⁻ + H₂O₂ ⇄ OH* + OH⁻ 0.71Reactions that Create Hydrogen Peroxide through the Forced Reduction ofDioxygen in a PHPG Reactor, but not in a Concentrated Plasma Reactore⁻ + O₂ ⇄ O₂ ⁻ (First Step is non-Spontaneous) −0.13 2H⁺ + 2e⁻ + O₂ ⇄H₂O₂ (Overall Reaction) 0.70 Other Reactions Common in a ConcentratedPlasma Reactor, but which do not take place in a PHPG Reactor, whichdoes not use Ozone- Producing Wavelengths of Light O₂ + hv ⇄ 2O* (byPhotolysis) ≤−5.13 2O* + 2O₂ ⇄ 2O₃ 2.99 O₃ + 2H⁺ + 2e⁻ ⇄ O_(2(g)) + H₂O2.075 O₃ + H₂O + 2e⁻ ⇄ O_(2(g)) + 2OH- 1.24 Ozone Destruction ofHydrogen Peroxide O₃ + H₂O₂ ⇄ H₂O + 2O₂ 1.381

Additionally, several side reactions generate a variety of species thatbecome part of the photocatalytic plasma, and which inhibit theproduction of PHPG for release into the environment as noted above.

In general, hydroxyl radicals are produced by the oxidation of water andrequire an oxidation potential of at least 2.85 eV to take place. Thecatalyst, therefore, must be activated by photons with at least thisrequired energy. Photons with lower energy than 2.85 eV will not producehydroxyl radicals, but photons with energy of at least 1.71 eV canphotolyse hydrogen peroxide into hydroxyl radicals. Excess light withenergy of 1.71 eV or above should be avoided due to the destruction ofhydrogen peroxide.

Inside a plasma reactor, where it is possible for free electrons torecombine with hydroxyl radicals and form hydroxide ions, this is thethermodynamically favored reaction because it has the highest reductionpotential, 2.02 eV. All reactions with lower reduction potentials, suchas the combination of hydroxyl radicals to form hydrogen peroxide, 1.77eV, are not favored. In rare instances where the formation of hydrogenperoxide occurs, a stoichiometric excess of two free electrons will becreated. In this case the stoichiometric excess of free electrons makesit possible for lower potential reactions to take place, most notablythe reduction of the hydrogen peroxide molecule into a hydroxyl radicaland a hydroxide ion, 0.71 eV, then further down to water by separatereduction of the radical and of the ion.

In a plasma reactor, the abundance of free electrons ensures that thereduction of hydroxyl radicals dominates, and that any hydrogen peroxidethat may theoretically be formed is immediately reduced back into water.

In contrast, in a PHPG reactor, production of hydrogen peroxide isfavored because the reactor separates hydroxyl radicals from the freeelectrons, preventing the reduction of the hydroxyl radicals to water.This permits the next most favored reaction to take place, thecombination of hydroxyl radicals to form hydrogen peroxide. The hydrogenperoxide can be reduced back down to water by decomposition (reaction ofhydrogen peroxide molecules with each other), but this effect isminimized by ensuring that the hydrogen peroxide produced is dilute.

Also, since the PHPG reactor separates hydroxyl radicals from the freeelectron remaining on the catalyst, the free electrons are forced toreduce another species, in this case dioxygen. The reduction of dioxygento the superoxide ion has a negative reduction potential, −0.13 eV,which indicates that it is non-spontaneous, but only slightly so. Thenon-spontaneity is overcome by the build-up of free electrons on thecatalyst, creating an increasing thermodynamic reduction pressure. Thisnon-spontaneous reaction is the first of four steps in the reduction ofoxygen to hydrogen peroxide, the remaining three of which are allspontaneous. It is important to note that when all four of these stepsare combined into a single reduction reaction, the overall potential ispositive, or spontaneous. It is easy to overlook the fact that thenon-spontaneous first step must take place in order for the threeremaining spontaneous steps to follow.

The reduction of dioxygen to hydrogen peroxide, forced by the removal ofhydroxyl radicals from the free electrons remaining on the catalyst,results in the desired production of yet more hydrogen peroxide, ofcourse.

The reactions listed in Table 1 are the most pertinent. Other reactions,known in the art can be added and their relative contributions reactionson the catalyst surface determined by their relative potentials comparedto the key reactions. Notably, as in the formation of ozone by plasmareactors, another high potential reaction is introduced that destroyshydrogen peroxide. To completely avoid ozone production, one need onlyavoid the use of light at wavelengths of 186 nm and below.

The wavelengths of light used to activate photocatalysts are alsoenergetic enough to photolyse the peroxide bond in a hydrogen peroxidemolecule and are also an inhibitor in the production of PHPG for releaseinto the environment. Further, the practice of using wavelengths oflight that produce ozone introduces yet another species into thephotocatalytic plasma that destroys hydrogen peroxide.O₃+H₂O₂⇄H₂O to 2O₂

In practice, photocatalytic applications have focused on the productionof a plasma, often containing ozone, used to oxidize organiccontaminants and microbes. Such plasmas are primarily effective withinthe confines of the reactor itself, by nature have limited chemicalstability beyond the confines of the reactor, and actively degrade thelimited amounts of hydrogen peroxide gas that they may contain. Further,because the plasma is primarily effective within the reactor itself,many designs maximize residence time to facilitate more completeoxidation of organic contaminants and microbes as they pass through thereactor. Since hydrogen peroxide has such a high potential to bereduced, the maximized residence time results in minimized hydrogenperoxide output.

Also, most applications of photocatalysis produce environmentallyobjectionable chemical species. First among these is ozone itself, anintentional product of many systems. Further, since organic contaminantsthat pass through a reactor are seldom oxidized in one exposure,multiple air exchanges are necessary to achieve full oxidation to carbondioxide and water. As incomplete oxidation occurs, a mixture ofaldehydes, alcohols, carboxylic acids, ketones, and other partiallyoxidized organic species is produced by the reactor. Often,photocatalytic reactors can actually increase the overall concentrationof organic contaminants in the air by fractioning large organicmolecules into multiple small organic molecules such as formaldehyde.

Methods of vaporizing aqueous hydrogen peroxide solutions produce, atbest, hydrated forms of hydrogen peroxide. Also, though photocatalyticsystems are capable of producing hydrogen peroxide, they have multiplelimitations that severely inhibit PHPG production for release into theenvironment. We have previously disclosed methods and devices forproducing PHPG in U.S. application Ser. No. 12/187,755, published May 1,2012, as U.S. Patent Publication No. 2009/0041617, and herebyincorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

The present application provides for and includes improved devices andmethods for generating Purified Hydrogen Peroxide Gas (PHPG).

SUMMARY OF THE INVENTION

The present disclosure provides for, and includes, improved devices forproducing non-hydrated purified hydrogen peroxide gas (PHPG) comprisingan enclosure, an air distribution mechanism providing an airflow, anair-permeable substrate structure having a catalyst on its surface, asource of light, wherein the airflow is through said air-permeablesubstrate structure and the device produces PHPG and directs it out ofsaid enclosure when in operation.

The present disclosure provides for, and includes, a device forproducing non-hydrated purified hydrogen peroxide gas (PHPG) wheninstalled into a heating, ventilating, and air conditioning (HVAC)system comprising an air-permeable substrate structure having a catalyston its surface and a source of light wherein air flows from the HVACsystem through the air-permeable substrate structure and the deviceproduces PHPG and directs it away from the air-permeable substratestructure when in operation and into a heated, ventilated and airconditioned space.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C are illustrations of an embodiment of the presentdisclosure designed to be installed as part of an HVAC system. Notably,the enclosure and air distribution mechanism are provided by the HVACsystem (e.g., the ductwork and system fans respectively).

FIGS. 2A to 2C are illustrations of an exemplary stand alone PHPGgenerating device according the present disclosure.

DETAILED DESCRIPTION

Before explaining aspects of the invention in detail, it is to beunderstood that the invention is not necessarily limited in itsapplication to the details set forth in the following description orexemplified by the Examples. The invention is capable of other aspectsor of being practiced or carried out in various ways.

The present disclosure provides for and includes devices for producingnon-hydrated purified hydrogen peroxide gases (PHPG). In aspectsaccording to the present disclosure, a device for producing non-hydratedpurified gas includes an enclosure, an air distribution mechanism, asource of ultraviolet light, an air-permeable substrate structure havinga catalyst on its surface wherein the airflow passes through theair-permeable substrate structure and directs the PHPG produced by thedevice out of the enclosure when the device is in operation.

In aspects according to the present disclosure, the device produces PHPGand directs the PHPG gas out of the enclosure. Not to be limited bytheory, the production of PHPG gas is rate limited and governed by therate of adsorption of humidity from the air onto the active sites forthe catalyst. Accordingly, the maximal rate of PHPG gas production isbelieved to be humidity dependent and can be calculated assuming thefollowing conditions: 1. a fully hydrated catalyst; 2. sufficient lightintensity to provide full activation of the catalyst; 3. 100% productionwith no losses due to hydrogen peroxide photolysis or hydrogen peroxidedecomposition; and 4. a large excess of oxygen to be reduced. Since twophotons produce two hydroxyl radicals, two free electrons, and twohydrogen ions, and an oxygen molecule is readily available, two hydrogenperoxide molecules are produced. Therefore the ratio of photons used tohydrogen peroxide molecules produced is 1:1 under wildly idealcircumstances. On a P25 grade of TiO₂ there are up to 14×10¹⁴ activesites per square centimeter. On a P90 grade of TiO₂ there are up to42×10¹⁴ active sites per square centimeter. So, at best, a fullyhydrated catalyst can produce 42×10¹⁴ molecules of hydrogen peroxideimmediately using adsorbed water. After that, the rate of productionwill be governed by the rate at which new water is adsorbed onto thecatalyst, which is humidity dependent.

In another aspect, the device produces PHPG at a rate sufficient toestablish a steady state concentration of PHPG of at least 0.005 ppm ina closed air volume of 10 cubic meters.

In an aspect, the device produces a concentration of at least 0.005 ppmin an air volume of 10 cubic meters (m³) wherein 10 percent of the airvolume is replaced with fresh, non-PHPG containing air each hour.

In aspects according to the present disclosure, hydrogen peroxide gasmay be measured in a volume of air. Since no device is yet readilyavailable to measure hydrogen peroxide gas at levels below 0.10 ppm,methods to measure the amount of hydrogen peroxide over time or methodsemploying a calibrated pump may be employed. In an aspect, a hydrogenperoxide test strip normally used to measure approximate concentrationsin aqueous solution can be used to detect the presence of PHPG overtime. In an aspect, a hydrogen peroxide test strip can measure theaccumulated PHPG up to one hour to provide approximate readings of PHPGconcentration accurate to within 0.01 ppm. In certain aspects, a teststrip that accumulates 0.5 ppm over the course of five minutes whenexposed for 15 twenty-second intervals, indicates an approximateconcentration of 0.033 ppm (e.g., 0.5 ppm divided by 15). In otheraspects, a Draeger tube, designed to detect hydrogen peroxideconcentrations as low as 0.10 ppm after drawing 2000 cubic centimetersof air using a calibrated pump, provides readings of lowerconcentrations accurate within 0.005 ppm using larger volumes of air formeasurement. In certain aspects, a Draeger tube indicating a measure ofPHPG at 0.10 ppm after drawing in 4000 cubic centimeters provides aconcentration of 0.05 ppm. In another aspect, a Draeger tube thatindicated 0.10 ppm after drawing 6000 cubic centimeters, measures anapproximate PHPG concentration of 0.033 ppm.

According to the present disclosure, non-hydrated purified hydrogenperoxide gas (PHPG) comprises gaseous hydrogen peroxide (H₂O₂) that issubstantially free of hydration, ozone, plasma species, or organicspecies.

As used herein, the term “substantially free of ozone” means an amountof ozone below about 0.015 ppm ozone. In an aspect, “substantially freeof ozone” means that the amount of ozone produced by the device is belowor near the level of detection (LOD) using conventional detection means.Ozone detectors are known in the art and have detection thresholds inthe parts per billion using point ionization detection. A suitable ozonedetector is the Honeywell Analytics Midas® gas detector capable ofdetecting 0.036 to 0.7 ppm ozone.

As used herein, substantially free of hydration means that the hydrogenperoxide gas is at least 99% free of water molecules bonded byelectrostatic attraction and London Forces.

Also as used herein, a PHPG that is substantially free of plasma speciesmeans hydrogen peroxide gas that is at least 99% free of hydroxide ion,hydroxide radical, hydronium ion, and hydrogen radical.

As used herein the term “higher” refers to at least about 3%, 5%, 7%,10%, 15%, 20%, 25%, 30%, 50%, 60%, 70%, 80%, 90%, or even a few foldshigher.

As used herein the term “improving” or “increasing” refers to at leastabout 2%, at least about 3%, at least about 4%, at least about 5%, atleast about 10%, at least about 15%, at least about 20%, at least about25%, at least about 30%, at least about 35%, at least about 40%, atleast about 45%, at least about 50%, at least about 60%, at least about70%, at least about 80%, at least about 90%, or greater increase.

As used herein the term “about” refers to ±10%.

The terms “comprises,” “comprising,” “includes,” “including,” “having,”and their conjugates mean “including but not limited to.”

The term “consisting of” means “including and limited to.”

The term “consisting essentially of” means that the composition, method,or structure may include additional ingredients, steps, and/or parts,but only if the additional ingredients, steps, and/or parts do notmaterially alter the basic and novel characteristics of the claimedcomposition, method, or structure.

As used herein, the singular form “a,” “an,” and “the” include pluralreferences unless the context clearly dictates otherwise. For example,the term “a compound” or “at least one compound” may include a pluralityof compounds, including mixtures thereof.

Whenever a numerical range is indicated herein, it is meant to includeany cited numeral (fractional or integral) within the indicated range.The phrases “ranging/ranges between” a first indicate number and asecond indicate number and “ranging/ranges from” a first indicate number“to” a second indicate number are used herein interchangeably and aremeant to include the first and second indicated numbers and all thefractional and integral numerals there between.

As used herein the term “method” refers to manners, means, techniques,and procedures for accomplishing a given task including, but not limitedto, those manners, means, techniques, and procedures either known to orreadily developed from known manners, means, techniques, and proceduresby practitioners of the agronomic, chemical, pharmacological,biological, biochemical, and medical arts.

In aspects according to the present disclosure, an enclosure comprises avolume having at least one opening for the entry of air and at least oneopening for the discharge of air having non-hydrated purified hydrogenperoxide gas. In an aspect, the enclosure may be made of plastic, metal,wood, or glass. According to some aspects, the enclosure may be opaque.In other aspects, the enclosure may be opaque to ultraviolet light andprovide for the transmission of light in the visible spectrum. In anaspect, the enclosure may further include a reflective surface on theinside of the device to reflect light back to the air-permeablesubstrate structure having a catalyst and thereby increase theproduction of non-hydrated purified hydrogen peroxide gas. In an aspect,an enclosure may comprise a material resistant to degradation byultraviolet light. In aspects according to the present disclosure, theenclosure may be prepared from plastics selected from the groupconsisting of acrylic, polyester, silicone, polyurethane, andhalogenated plastic. In some aspects, the enclosure may be prepared froma ceramic or porcelain. In some aspects, the enclosure may be preparedfrom polyethylene, polypropylene, polystyrene, nylon, or polyvinylchloride.

As used herein, in other aspects, an enclosure can comprise a heating,ventilating, and air conditioning (HVAC) system. Referring to FIGS. 1Ato 1C, a device for producing PHPG is a device placed within an existingHVAC system comprising an air-permeable substrate structure 102 having acatalyst on its surface and a source of light 104 as recited below Inother aspects, a device for producing PHPG is a device placed in an HVACsystem during construction. An aspect of a PHPG producing devicesuitable for incorporation into an HVAC system is illustrated in FIGS.1A to 1C. As illustrated, a suitable device can be installed into anexisting HVAC system that having a rectangular duct according toapplicable national and international standards. Suitable HVAC systemsand appropriate standards are known in the art, for example standardsdeveloped by the Sheet Metal & Air Conditioning Contractors' NationalAssociation (SMACNA). For example, the American National StandardsInstitute (ANSI) has accredited SMACNA as a standard-settingorganization. As provided herein, devices suitable for installation intoan HVAC system include the elements recited for standalone devices butwherein the enclosure and air distribution system are provided by theHVAC system. Devices suitable for installation into an HVAC system mayfurther comprise an additional air distribution system (e.g., separatefrom the air distribution system of the HVAC system as a whole). Devicessuitable for installation into an HVAC system may further comprise oneor more additional filters to prevent contamination with dust orchemicals.

In aspects according to the present disclosure, a device includes an airdistribution mechanism to provide an airflow. In some aspects, the airflow is a continuous airflow. In other aspects, the air flow isdiscontinuous. In aspects according to the present disclosure, theairflow of the device may be a laminar flow of air though anair-permeable substrate structure. In other aspects, the airflow may beturbulent flow through an air-permeable substrate. In yet anotheraspect, the airflow may be transitional. In aspects according to thepresent disclosure, the airflow of the device may have a Reynolds numberof less than 2300. In another aspect, the airflow of the device may havea Reynolds number of between 2300 and 4000. In yet another aspect, theairflow of the device may have a Reynolds number of greater than 4000.

In some aspects, an air distribution mechanism is placed upstream of anair permeable substrate structure and provides an airflow through theair permeable substrate. In other aspects, an air distribution mechanismis placed after an air permeable substrate and pulls the air through thesubstrate. In certain aspects, the airflow is provided by one or morefans. In certain aspects, the airflow may be provided by a source ofcompressed air. In an aspect, the source of compressed air may be a tankof compressed air. In other aspects, the compressed air may be providedby an air compressor and storage tank. In yet another aspect, the airflow is provided by a climate control system such as an air conditioner,a furnace, or a heating, ventilation, and air-conditioning (HVAC)system.

In aspects according the present disclosure, the device may provide anairflow having a velocity, a direction, and an angle of incidencerelative to the air permeable substrate structure.

Devices of the present disclosure are provided with an airflowsufficient to minimize the time of contact with the photocatalyticsurface. More specifically, devices of the present disclosure aredesigned to minimize the contact of hydrogen peroxide gas generatedduring photocatalysis with the photocatalytic substrate in order tominimize the degradation of the hydrogen peroxide by contaminatingozone, hydroxide ions, hydroxide radicals, hydronium ions, and hydrogenradicals. This minimization of ozone production and contact is incontrast with “air purification” filters and devices employing similarphotocatalytic principles. In contrast to devices of the presentdisclosure, air purifiers and filters are designed to maximize thecontact of the air with the catalytic surface and the photocatalyticplasma. Even further, prior filters and purifiers are designed to actwithin an enclosed volume and are designed not to expel PHPG but rather‘clean’ air having volatile organic compounds (VOC's), bacteria,microbes, spores, viruses, and other undesirable contaminants destroyedor reduced. Similarly, prior filters and purifiers are concerned withthe production of ozone and/or hydroxide radicals, each of which isundesirable in devices of the present disclosure.

The devices of the present disclosure include and provide for airdistribution mechanisms capable of providing an airflow having avelocity from about 5 nanometers/second (nm/s) to 10,000 nm/s asmeasured at the surface of the air permeable substrate structure. Incertain aspects, the flow rate is between 5 nm/s to 7,500 nm/s. Incertain aspects, the flow rate is between 5 nm/s to 5,000 nm/s. Incertain aspects, the flow rate is between 5 nm/s to 2,500 nm/s. Incertain aspects, the flow rate is between 5 nm/s to 5,000 nm/s. Incertain aspects, the flow rate is between 5 nm/s to 1,000 nm/s. In otheraspects, the flow rate of the air at the air permeable substratestructure is between 5 and 15 nm/s. In another aspect, the air flowvelocity is between 15 nm/s to 30 nm/s. In an aspect, the air flowvelocity is between 30 nm/s to 50 nm/s. In an aspect, the air flowvelocity is between 50 nm/s to 75 nm/s. In an aspect, the air flowvelocity is between 75 nm/s to 100 nm/s. In an aspect, the air flowvelocity is between 100 nm/s to 250 nm/s. In an aspect, the air flowvelocity is between 250 nm/s to 500 nm/s. In an aspect, the air flowvelocity is between 500 nm/s to 750 nm/s. In an aspect, the air flowvelocity is between 750 nm/s to 1000 nm/s. In an aspect, the air flowvelocity is between 1000 nm/s to 2,500 nm/s. In an aspect, the air flowvelocity is between 2,500 nm/s to 5,000 nm/s. In an aspect, the air flowvelocity is between 5,000 nm/s to 7,500 nm/s. In an aspect, the air flowvelocity is between 7,500 nm/s to 10,000 nm/s. As provided herein, themaximal airflow through the air permeable structure is limited by thereaction of hydroxyl radicals into hydrogen peroxide and the productionrate of PHPG drops. Not to be limited by theory, it is thought that thehydroxyl radicals are maintained in a sufficiently dilute balance whichfavors their combination to form hydrogen peroxide yet minimizesdecomposition into water and oxygen. The maximal flow limitation dependson the air permeable structure, the catalyst, the relative humidity andother variables and one of ordinary skill in the art can readily adjustthe airflow to maximize PHPG production. In certain aspects, suitabledevices for HVAC systems are designed to handle air flows up to 40,000cubic feet per minute (CFM).

The present disclosure provides for, and includes, airflow rates throughthe air permeable substrate structure of greater than 100 CFM. In anaspect, PHPG generating devices for an HVAC system are provided anairflow on average of 145 CFM. For a standalone PHPG generating device,the air distribution mechanism provides for an average of 115 CFMthrough the air permeable substrate structure.

The present disclosure also includes and provides for devices having anair flow velocity sufficient to provide a residence time on the catalystsurface of less than 1 second. One of ordinary skill in the art wouldunderstand that the time available at a catalyst surface is affected by,among other parameters, the air velocity, the angle of incidence, andthe thickness of the substrate. In aspects according to the presentdisclosure, the device provides a residence time on the catalyst surfaceof an air permeable substrate of less than 2 seconds. In an aspect, theresidence time is less than 1 second. In some aspects, the residencetime is less than 500 ms. In a further aspect, the residence time isless than 250 ms. In yet another aspect, the residence time is between 1and 500 ms.

In aspects, the direction of the airflow at the air permeable structuremay be provided at an angle relative to the air permeable structure (theangle of incidence). In contrast to the present disclosure, the PHPGproducing devices disclosed in U.S. Pat. Nos. 8,168,122, 8,684,329 and9,034,255, provide a diffuser apparatus for producing non-hydratedpurified peroxide gas (PGPG) from humid ambient air having an airflowperpendicular to a thin air permeable substrate structure. Here, we showthat production of PHPG can be achieved using air flows that areincident to the air permeable substrate at angles of at least 14°. Notto be limited by theory, the permissible angle of incidence is believedto be related to the thickness of the air permeable substrate structureand the velocity of airflow. As the thickness of the substrate structureis reduced, the incident angle may also be reduced, starting at 90°(airflow to substrate angle) which provides the optimal condition forthe production of PHPG by maintaining a short residence time of hydrogenperoxide on the substrate surface. Similarly, the angle of incidence maybe reduced for a given thickness of substrate as the velocity of theairflow is increased, though angles below 14° did not result in theproduction of detectable levels of PHPG. Not to be limited by theory,the rate of PHPG production is maximal at an angle of incidence of 90°and essentially non-detectable when the angle of incidence of theairflow is at about 14 degrees or less. Between about 14° C. and 68° C.,the production of PHPG increases steadily. Unexpectedly, at angles ofincidence as low as 68° C. suitable levels of PHPG are produced, andconsistent with previous reports, optimal production occurs when theairflow is perpendicular. Accordingly, devices in the art that havecatalytic surfaces that are parallel to the airflow do not produce PHPG,even if the incident light is perpendicular. Thus, devices in the artdesigned to generate ozone, peroxide and other reactive species within areactor do not produce PHPG and do not direct PHPG outside of thereactor.

In certain aspects, the airflow may be provided at an incident angle of90° relative to the air permeable substrate structure (e.g.,perpendicular to the air permeable substrate). In devices having anincident angle of 90°, the residence time of the non-hydrated purifiedhydrogen peroxide gas is minimal for a given airflow and substratethickness. In aspects according to the present disclosure, the minimalincident angle is 14°. In other aspects, the incident angle of theairflow relative to the air permeable structure is at least 45° orgreater. In another aspect, the incident angle is greater than 50°. Inyet another aspect, the incident angle is greater than 60°. In a furtheraspect, the incident angle is greater than 70°. In another aspect, theincident angle is greater than 75°. In an aspect, the incident angle maybe greater than 80°. In a further aspect, the incident angle may begreater than 85°. In yet another aspect, the incident angle may begreater than 89°. In aspects according to the present disclosure, theincident angle of the airflow may be between 68° and 90° relative to thesubstrate structure. In other aspects, the incident angle of the airflowmay be between 75° and 90° relative to the substrate structure. In otheraspects, the incident angle of the airflow may be between 85° and 90°relative to the substrate structure.

In aspects according to the present disclosure, the airflow through theair permeable substrate structure is humid air. In certain aspects, thehumid air is ambient humid air. In other aspects, the humidity of theair flowing through the air permeable substrate is at or above 20% RH.In further aspects, the humidity of the air flowing through the airpermeable substrate is at or above 30%. In some aspects, the relativehumidity is between 35% and 40%. In other aspects, the humidity of theambient air may be between about 20% and about 99% RH. In other aspects,the humidity of the ambient air may be between about 20% and about 99%RH. In certain aspects, the humidity of the air flow is less than 80%.In an aspect, the humidity is between 20% and 80%. In yet other aspects,the relative humidity is between 30% and 60%. In another aspect, thehumidity is between 35% and 40%. In some aspects, the humidity of theair flowing through the air permeable substrate structure is between 56%and 59%. In aspects according to the present disclosure the relativehumidity is between 20% and 80%.

In aspects according to the present disclosure, the airflow through theair permeable substrate structure may be supplemented by humidification.In certain aspects, ambient air is supplemented by a humidifier toprovide an airflow having at least 20% humidity. In certain aspects, therelative humidity of the air flowing through permeable substratestructure is maintained at between 20% and 80%. In another aspect, theair may be humidified to 30% or higher relative humidity. In someaspects, the relative humidity of the humidified airflow is between 35%and 40%. In other aspects, the humidity of the humidified air may bebetween about 20% and about 99% or between about 30% to 99% RH. In anaspect, the relative humidity after humidification is less than 80%. Inan aspect, the relative humidity after humidification is between 20% and80%. In yet other aspects, the relative humidity after humidification isbetween 30% and 60%. In another aspect, the relative humidity afterhumidification is between 35% and 40%. In some aspects, the relativehumidity after humidification of the air flowing through the airpermeable substrate structure is between 56% and 59%.

In aspects according to the present disclosure, a device may provide anairflow that recirculates air within a space. In other aspects, a devicemay provide, in whole or in part, an airflow comprising fresh air. Incertain aspects, the device includes and provides for a source of freshair either from the outside or from a separate filtered flow of air. Inaspects according to the present disclosure, the device may be includedin an air conditioning and ventilation system that recirculates airwithin a room or building. In some aspects, the recirculating room orbuilding air may be supplemented with fresh outside air.

The devices of the present disclosure include an air permeable substratestructure having a catalyst on the surface configured to producenon-hydrated purified hydrogen peroxide gas when exposed to a lightsource and provided an airflow. The substrate structure can vary inthickness, air permeability, and surface catalyst. In certain aspects,the substrate structure may be thicker or thinner depending on the rateof air flow, the incident angle of the air flow, the intensity of thelight, and the type of catalyst. The selection of thickness, air flow,air flow angle, and other parameters is to provide a substrate surfacemorphology to minimize the residence time of hydrogen peroxide moleculeson the surface of the air permeable substrate structure. Not to belimited by theory, it is thought that hydrogen peroxide gas generated onthe substrate surface is released from the surface and thereby preventedfrom being reduced back into water by the substrate or hydroxide.

In aspects according to the present disclosure, the air permeablesubstrate structure having a catalyst on its surface is between about 5nanometers (nm) and about 750 nm in total thickness. In certain aspects,the maximum thickness of an air permeable substrate structure is 650 nm.In an aspect, the thickness of the air permeable substrate structure isbetween 100 and 200 nm. In an aspect, the thickness of the air permeablesubstrate structure is between 145 and 150 nm. In an aspect, thethickness of the air permeable substrate structure is between 5 nm and15 nm. In another aspect, the thickness of the air permeable substratestructure is between 15 nm and 30 nm. In an aspect, the thickness of theair permeable substrate structure is between 20 nm and 40 nm. In anaspect, the thickness of the air permeable substrate structure is about30 nm. In a further aspect, the thickness of the air permeable substratestructure is between 30 nm and 50 nm. In yet another aspect, thethickness of the air permeable substrate structure is between 50 nm and75 nm. In an aspect, the thickness of the air permeable substratestructure is between 75 nm and 100 nm. In yet another aspect, thethickness of the air permeable substrate structure is between 100 nm and250 nm. In a further aspect, the thickness of the air permeablesubstrate structure is between 250 nm and 500 nm. In certain aspects,the thickness of the air permeable substrate structure is between 500 nmand 750 nm. In aspects according to the present disclosure, thethickness of the air permeable substrate structure having a catalyst onits surface is between about 5 nm and 100 nm. In an aspect, thethickness of the air permeable substrate structure having a catalyst onits surface is between about 15 nm and 100 nm. In an aspect, thethickness of the air permeable substrate structure having a catalyst onits surface is between about 20 nm and 100 nm. In an aspect, thethickness of the air permeable substrate structure having a catalyst onits surface is between about 20 nm and 75 nm. In an aspect, thethickness of the air permeable substrate structure having a catalyst onits surface is between about 20 nm and 50 nm.

In certain aspects according to the present disclosure, the airpermeable substrate structure having a catalyst on its surface isbetween about 750 nanometers (nm) and about 1000 nm in total thickness.In an aspect, the thickness of the air permeable substrate structure isbetween 1000 and 2500 nm. In another aspect, the thickness of the airpermeable substrate structure is between 2500 nm and 5000 nm. In anaspect, the thickness of the air permeable substrate structure isbetween 5000 nm and 7500 nm. In a further aspect, the thickness of theair permeable substrate structure is between 7500 nm and 10000 nm.

Also provided for and included in the present disclosure are deviceshaving an air permeable substrate structure configured as a mesh. Asused herein, a “mesh” refers to a network of spaces in a net or networkcomprising a network of cords, threads, or wires. In some aspects, amesh may be a woven cloth or fabric. In some aspects, a mesh may be awoven stainless steel. In certain aspects, a mesh may be a wovenstainless steel shaped as honeycombs. In other aspects, a mesh may be anonwoven cloth or fabric. In certain aspects, a mesh may be preparedfrom a solid sheet by introducing holes or perforations eithermechanically, thermally, or chemically. In an aspect, a mesh may beprepared from a film.

In the course of developing devices of the present disclosure, it isobserved that air permeable substrate structures require a mesh havingat least 20% open area in order to generate effective amounts of PHPG.Similarly, when the open area of the mesh is greater than 60%, PHPGgeneration is essentially eliminated. Accordingly, the presentdisclosure provides for and includes, air permeable substrate structureshaving a mesh with an open area of between 20% and 60% and a maximalthickness of up to 750 nm. Suitable thicknesses of air permeablesubstrates are provided above. Also included are air permeable substratestructures having a mesh with an open area of about 40%. In an aspectthe mesh opening is about 200 microns and the thread thickness is about152 microns.

Additional testing revealed that non-woven fabrics are not suitable forthe preparation of air permeable substrates coated with a catalyst. Notto be limited by theory it is thought that the inability to identifysuitable non-woven materials results from the irregular or insufficientmesh of the non-woven materials. However, it is believed that suitablenon-woven materials can be prepared. Accordingly, included and provideby the present disclosure are non-woven air permeable substratestructures having a mesh of between 20 and 60% and a thickness of lessthan 750 nm that are useful in the preparation of PHPG generatingdevices.

In aspects according to the present disclosure, a mesh is greater than20 strands per centimeter. In certain aspects, the open area of the meshis less than about 120 strands per centimeter. In an aspect, the meshopening is about 200 microns (μm) corresponding to about 41% open areafor a thread thickness of about 150 microns. In certain aspects, themesh includes an open area of at least about 20% and a thread thicknessof about 48 microns. In certain aspects, the mesh has a hole size ofbetween 25 μm and 220 μm and having an open area of between 20% and 40%.In other aspects, the mesh has a hole size of between 25 μm and 220 μmand a thread thickness of between 48 μm and 175 μm.

In aspects according to the present disclosure, a mesh may be preparedhaving a regular, repeating pattern of spaces in the net or network. Inother aspects, a mesh of the present disclosure may have an irregular ornon-repeating pattern of spaces. In yet another aspect, the mesh may bea random array of open spaces. In another aspect, the mesh may have ahoneycomb appearance. In aspects according to the present disclosure,the open spaces within the mesh are round, triangular, square,polygonal, polyhedron, ellipsoid, or spherical.

An air permeable substrate structure of the present disclosure can beprepared from a number of suitable materials. In certain aspects, an airpermeable substrate structure may comprise a catalyst. In other aspects,an air permeable substrate structure may comprise a catalyst and aco-catalyst. In yet other aspects, an air permeable substrate structuremay comprise a catalyst, a co-catalyst, and an additive. In certainaspects, an air permeable substrate structure may be prepared as aceramic. In yet other aspects, the air permeable substrate structureconsists solely of the catalyst or catalyst/co-catalyst combination.

The present disclosure also provides for air permeable substrates thatare coated. In some aspects, an air permeable substrate structure maycomprise a material that is coated with one or more catalysts. In otheraspects, an air permeable substrate structure may comprise a materialthat is coated with a catalyst and one or more co-catalysts. In yetanother aspect, an air permeable substrate structure may comprise amaterial that is coated with a mixture of a catalyst, co-catalyst, andan additive.

Methods for coating an air permeable substrate are known in the art. Incertain aspects, an air permeable substrate is coated with a crystallinetitanium dioxide powder in one or more applications and sintered in anoven. The coatings of the present disclosure may be applied to a mesh bya variety of methods including, but not limited to, gel sol methods,painting, dipping, and powder coating. In other aspects, the catalysts,co-catalysts and additives of the present disclosure may be applied to amesh by toll coating, tape casting, ultrasonic spray and web-basedcoating. As provided herein, the method of applying the catalysts,co-catalysts and additives is suitable if it provides for, and includes,retaining the mesh of the underlying air permeable substrate as recitedabove.

According to the present disclosure, an air permeable substratestructure comprises a mesh having a percentage of open area of between20% and 60% after coating. In another aspect, the mesh may have an openarea of between 20% and 30%. In an aspect, the mesh may have an openarea of between 30% and 40%. In a further aspect, the mesh may have anopen area of between 40% and 50%. In yet another aspect, the mesh mayhave an open area of between 50% and 60%. In certain aspects, thepercentage of open area of the mesh may be between 36% and 38%. In anaspect, the percentage of open area is about 37%.

The present disclosure provides for and includes for air permeablesubstrate structures having a thickness of between 5 nm and 750 nm andhaving an open area of a mesh between 10% and 60%. In an aspect, thesubstrate structure may have a thickness selected from the groupconsisting of 5 nm to 15 nm, 15 nm to 30 nm, 20 nm to 40 nm, 30 nm to 50nm, 50 nm to 75 nm, 75 nm to 100 nm, 100 nm to 250 nm, 250 nm to 500 nm,and 500 nm to 750 nm and having an open area of mesh between 10% and20%. In an aspect, the substrate structure may have a thickness selectedfrom the group consisting of 5 nm to 15 nm, 15 nm to 30 nm, 20 nm to 40nm, 30 nm to 50 nm, 50 nm to 75 nm 75 nm to 100 nm, 100 nm to 250 nm,250 nm to 500 nm, and 500 nm to 750 nm thick and has an open area ofmesh between 20% and 30%. In an aspect, the substrate structure may havea thickness selected from the group consisting of 5 nm to 15 nm, 15 nmto 30 nm, 20 nm to 40 nm, 30 nm to 50 nm, 50 nm to 75 nm, 75 nm to 100nm, 100 nm to 250 nm, 250 nm to 500 nm, and 500 nm to 750 nm thick andhas an open area of mesh between 30% and 40%. In an aspect, thesubstrate structure may have a thickness selected from the groupconsisting of 5 nm to 15 nm, 15 nm to 30 nm, 20 to 40 nm, 30 nm to 50nm, 50 nm to 75 nm, 75 nm to 100 nm, 100 nm to 250 nm, 250 nm to 500 nm,and 500 nm to 750 nm thick and has an open area of mesh between 40% and50%. In an aspect, the substrate structure may have a thickness selectedfrom the group consisting of 5 nm to 15 nm, 15 nm to 30 nm, 20 to 40 nm,30 nm to 50 nm, 50 nm to 75 nm, 75 nm to 100 nm, 100 nm to 250 nm, 250nm to 500 nm, and 500 nm to 750 nm thick and has an open area of meshbetween 50% and 60%. In an aspect, the substrate structure may have athickness selected from the group consisting of 5 nm to 15 nm, 15 nm to30 nm, 20 nm to 40 nm, 30 nm to 50 nm, 50 nm to 75 nm, 75 nm to 100 nm,100 nm to 250 nm, 250 nm to 500 nm, and 500 nm to 750 nm thick and hasan open area of mesh between 36% and 38%.

In other aspects, the air permeable substrate structure has a thicknessof between 15 nm and 250 nm and has an open area of a mesh between 20%and 50%. In another aspect, the air permeable substrate structure has athickness of between 15 nm and 100 nm and has an open area of a meshbetween 20% and 50%. In another aspect, the air permeable substratestructure has a thickness of between 20 nm and 80 nm and has an openarea of a mesh between 20% and 50%. In another aspect, the air permeablesubstrate structure has a thickness of between 20 nm and 50 nm and hasan open area of a mesh between 20% and 50%. In another aspect, the airpermeable substrate structure has a thickness of between 20 nm and 40 nmand has an open area of a mesh between 20% and 50%.

In other aspects, the air permeable substrate structure has a thicknessof between 15 nm and 250 nm and has an open area of a mesh between 30%and 50%. In another aspect, the air permeable substrate structure has athickness of between 15 nm and 100 nm and has an open area of a meshbetween 30% and 50%. In another aspect, the air permeable substratestructure has a thickness of between 20 nm and 80 nm and has an openarea of a mesh between 30% and 50%. In another aspect, the air permeablesubstrate structure has a thickness of between 30 nm and 50 nm and hasan open area of a mesh between 30% and 50%. In another aspect, the airpermeable substrate structure has a thickness of between 20 nm and 40 nmand has an open area of a mesh between 30% and 50%.

In other aspects, the air permeable substrate structure has a thicknessof between 20 nm and 40 nm and has an open area of a mesh between 10%and 60%. In another aspect, the air permeable substrate structure has athickness of between 20 nm and 40 nm and has an open area of a meshbetween 20% and 50%. In another aspect, the air permeable substratestructure has a thickness of between 20 nm and 40 nm and has an openarea of a mesh between 30% and 40%. In another aspect, the air permeablesubstrate structure has a thickness of between 20 nm and 40 nm and hasan open area of a mesh between 36% and 38%. In another aspect, the airpermeable substrate structure has a thickness of between 20 nm and 40 nmand has an open area of a mesh of about 37%.

Air permeable substrates suitable for coating with a catalyst mixture ofthe present disclosure are known in the art. In certain aspects, an airpermeable substrate comprises a solid sheet that is coated with acatalyst or catalyst containing mixture and then rendered air permeableby the introduction of holes or perforations as provided above. In otheraspects, an air permeable substrate comprises a solid sheet that hasbeen perforated and is subsequently coated with a catalyst or catalystmixture.

Suitable air permeable substrates for coating with a catalyst mixtureaccording to the present disclosure include meshes, such as woven clothor fabric or unwoven cloth or fabric. As provided herein, coating of asuitable mesh with a catalyst mixture requires that the mesh not beoccluded and that the mesh retain an open area of between 20% and 60% asprovided above.

Air permeable substrates of the present disclosure may be prepared frompolymers, carbon fibers, fiberglass, natural fibers, metal wires, andother materials that can be prepared as a mesh. Meshes may be wovenmeshes prepared from monofilament synthetic or natural fibers or yarns.In other aspects, woven meshes may be prepared from multifilamentsynthetic fibers or yarns. Woven meshes of the present disclosure may bedescribed by the thread count and have a thread diameter. Woven meshescomprise warp threads that run lengthwise in a woven mesh or fabric, andweft or filling threads that run across the width of a fabric at rightangles to the warp thread. In woven meshes comprising monofilaments,equal diameter threads and equal thread counts are present in both thewarp and weft directions and square mesh openings (or holes).Monofilament woven meshes may have different numbers of thread counts inthe warp and weft direction resulting in rectangular mesh openings.Woven meshes are available in a wide variety of thread counts.

Woven monofilament meshes suitable for devices of the present disclosurecomprise meshes having nominal hole sizes (e.g., mesh openings) rangingfrom 50 microns to 1200 microns. In an aspect, the woven monofilamentmesh suitable for coating as an air permeable substrate has a meshopening of between 100 and 300 microns. In another aspect, an airpermeable substrate is a woven monofilament mesh having an opening ofbetween 150 and 250 microns. In yet another aspect, an air permeablesubstrate is a woven monofilament mesh having a mesh opening of about200 microns. In an aspect, the woven monofilament mesh opening ofbetween 175 and 225 microns and a tread thickness of between 125 and 175microns. In yet another aspect, the woven monofilament mesh opening ofabout 200 microns and a tread thickness of about 152 microns.

In aspects according to the present disclosure, a mesh may be anextruded mesh (also called “extruded netting”). In an aspect, anextruded mesh may be a bi-planar extruded mesh. In another aspect, theextruded mesh may be a mono-planar mesh. Extruded mesh may comprise anetting having a variety of apertures (hole sizes), weights, andthicknesses. Extruded meshes may be prepared from polypropylene (PP),polyethylene (PE), high density polyethylene (HDPE), medium-densitypolyethylene (MDPE), low-density polyethylene (LDPE),polypropylene/polyethylene (PP/PE) blends, cross-linked polyethylene(PEX), ultra-high molecular weight polyethylene (UHMWPE).

In an aspect, a mesh suitable for coating according to the presentdisclosure is a fiberglass mesh or cloth. In some aspects, thefiberglass mesh is a fiberglass reinforced plastic (FRP). In someaspects, the fiberglass mesh is a woven mesh. Suitable woven fiberglassmeshes include fiberglass cloth, fiberglass chopped strand mat, wovenrovings. In some aspects, a fiberglass cloth is a combination of wovenroving and chopped strand mat. In another aspect, a fiberglass cloth isS-2 GLASS™. In some aspects, the fiberglass cloth is prepared using aplain weave, long shaft satin weave, unidirectional weave, or twillweave. In an aspect, a fiberglass cloth comprises E-glass. In anotheraspect, a fiberglass cloth comprises C-glass. In yet another aspect, afiberglass cloth comprises E-glass and C-glass. In some aspects, afiberglass mesh or cloth is combined with a resin to reinforce thefiberglass material. In one aspect, the resin is polyester. In anotheraspect, the resin is an epoxy.

In an aspect, a mesh suitable for coating according to the presentdisclosure is a polymer. In an aspect the mesh may be nylon,polybutylene terephthalate (PBT), polyester, polyethylene,polypropylene, polytetrafluoroethylene (PTFE),polypropylene/polyethylene (PP/PE) blends or synthetic yarns or fibers.

In aspects according to the present disclosure, a mesh may be preparedfrom natural fibers including cotton and wool. In some aspects, thenatural fiber is seed fiber, a leaf fiber, a bast fiber, a skin fiber, afruit fiber, or a stalk fiber. In other aspects, the natural fiber ishemp, sisal, jute, kenaf, or bamboo. In an aspect, the mesh may beprepared from silk.

Meshes according to the present disclosure may be a metal mesh or aceramic mesh. Suitable metal meshes include electroformed screens.Electroformed screens suitable for the preparation of catalyst coatedair permeable substrates according to the present disclosure areavailable from, for example, Industrial Netting (Minneapolis, Minn.).Electroformed screens may have hole sizes ranging from 8 microns to 5000microns or more. In certain aspects, the electroformed screen rangesfrom 36% to 98% open. In some aspects, the electroformed screen rangesfrom 36% to 98% open and has a thickness of between about 20 nm and 75nm.

The devices of the present disclosure provide for, and include, acatalyst on the surface of said air permeable substrate structures. Incertain aspects, a catalyst may be a catalyst mixture comprising one ormore catalysts. In other aspects, a catalyst mixture may comprise one ormore catalysts and one or more co-catalysts. In another aspect, acatalyst mixture may comprise one or more catalysts and one or moreadditives. In a further aspect, a catalyst mixture may comprise one ormore catalysts, one or more co-catalysts, and one or more additives.Catalyst mixtures may further comprise solubilizer, binders, viscositymodifiers, isotonizing agents, pH regulators, solvents, dyes, gellingagents, thickeners, buffers, and combinations thereof.

One of ordinary skill in the art would understand that the selection ofthe catalyst determines the type of photocatalysis that occurs uponillumination with a light source and further determines the wavelengthand intensity of light suitable for generating non-hydrated purifiedhydrogen peroxide gas. As discussed above, hydroxyl radicals produced byphotocatalysis must be removed from the catalytic surface before theyundergo reduction by free electrons on the catalyst or by other reactivespecies produced by photocatalysis. This forces them to combine to formhydrogen peroxide just beyond the catalyst. One of ordinary skill in theart would understand that the residence time of non-hydrated purifiedhydrogen peroxide gas on the air permeable substrate is determined bythe thickness of the substrate, the angle of incidence of the airflow,and the airflow velocity.

In aspects according to the present disclosure, the catalyst on thesurface of an air permeable substrate structure is a metal, a metaloxide, or mixtures thereof. Also provided for and included in thepresent disclosure are ceramic catalysts. Catalysts of the presentdisclosure include, but are not limited to, titanium dioxide, copper,copper oxide, zinc, zinc oxide, iron, iron oxide, or mixtures thereof.Suitable catalysts are provided, for example at Table 2. In someaspects, the catalyst is titanium dioxide in the form of anatase orrutile. In certain aspects, the titanium dioxide is the anatase form. Insome aspects, the catalyst is titanium dioxide in the form of rutile. Inother aspects, the titanium dioxide catalyst is a mixture of anatase andrutile. Anatase absorbs photons at wavelengths less than 380 nm, whereasrutile absorbs photons at wavelengths less than 405 nm. Also providedfor, are catalysts on the surface that comprise tungsten trioxide (WO₃)that provides for the use of a full spectrum of light with energies ofat least 2.85 eV. This extends the light source into the visible rangeof light beyond the range where TiO₂ is active alone. Not to be limitedby theory, WO₃ provides new energy levels that TiO₂ does not support andallows for the adsorption of visible light with sufficient energy tooxidize water to hydroxyl radicals. Accordingly, the present disclosurefurther provides for and includes, sources of light that providewavelengths in the visible range when paired with a suitable catalystsubstrate.

TABLE 2 Photocatalysts having suitable Band-gap Energies Band-gap energyPhotocatalyst (electron volts (eV)) Si 1.1 WSe₂ 1.2 CdS 2.4 WO₃ 2.4-2.8V₂O₅ 2.7 SiC 3.0 TiO₂ (rutile) 3.02 Fe₂O₃ 3.1 TiO₂ anatase 3.2 ZnO 3.2SRTiO₃ 3.2 SnO₂ 3.5 ZnS 3.6

In certain aspects, the catalyst may be tungsten oxide or a mixture oftungsten oxide with another metal or metal oxide catalyst. In someaspects, the catalyst is selected from the group consisting oftungsten(III) oxide, tungsten(IV) oxide (WO₂), tungsten(VI) oxide (WO₃),and tungsten pentoxide. In an aspect, the tungsten oxide is tungstendioxide (WO₂). In another aspect, the catalyst may be a tungstentrioxide (WO₃) catalyst combined with a cesium co-catalyst. (See“Development of a High-performance Photocatalyst that is Surface-treatedwith Cesium,” available on the internet atwww.aist.gojp/aist_e/latest_research/2010/20100517/20100517.html).

The catalysts of the present disclosure may further include one or moreco-catalysts. In certain aspects, co-catalysts provide light absorbingcapacity in the visible spectrum (e.g., wavelengths from about 390 nm to700 nm). Suitable catalysts and methods to prepare catalysts to providefor catalysts suitable for devices having a light source that emits inthe visible spectrum are known in the art. See, Tukenmez, “TungstenOxide Nanopowders and Its Photocatalytic Activity under Visible LightIrradiation,” Thesis, Department of Molecular Biology, Umea University,Sweden, (2013) available on the internet atwww.diva-portal.org/smash/get/diva2:643926/FULLTEXT01.pdf; Kim et al.,“Photocatalytic Activity of TiO₂ Films Preserved under DifferentConditions: The Gas-Phase Photocatalytic Degradation Reaction ofTrichloroethylene,” Journal of Catalysis 194(2):484-486 (2000); Blake etal., “Application of the Photocatalytic Chemistry of Titanium Dioxide toDisinfection and the Killing of Cancer Cells,” Separation andPurification Methods 28(1):1-50 (1999); Sugihara et al., “Development ofa Visible Light Responsive Photocatalyst using Tungsten Oxide underIndoor Lighting,” National Institute of Advanced Industrial Science andTechnology (AIST) (2008). Co-catalysts of the present disclosureinclude, but are not limited to, platinum, gold. silver, copper, nickel,cesium, or palladium. In some aspects, the co-catalyst is a noble metalselected from the group consisting of gold, platinum, silver, rhodium,ruthenium, palladium, osmium, and iridium. In an aspect, the co-catalystis gold. In another aspect, the co-catalyst is silver. In yet anotheraspect, the co-catalyst is platinum. In another aspect, the co-catalystis an extruded ceramic. In certain aspects, the co-catalyst is zirconiumdioxide (ZrO₂). In some aspects, the co-catalyst is an extruded titaniumdioxide ceramic (see Shon et al., “Visible Light Responsive TitaniumDioxide (TiO₂)—a review” available at epress.lib.uts.edu.au).

The present disclosure also includes substrate catalysts comprisingmetallic palladium, copper and WO₃ that provide for photocatalyticreactions to take place up to 460 nm into the visible spectrum andprovide a 7 fold increase in activity on the catalyst. In other aspects,the catalyst comprises a blend of WO₃ and TiO₂ that increases the photocatalytic reactions up to 60 fold at a wavelength of 410 nm. In afurther aspect, the blend of WO₃ and TiO₂ provides for a light sourcecomprising an XE lamp at 400 nm. In further aspects, the catalyst isspiked with nitrogen ions or WO₃ to provide for photocatalytic reactionsin within the visible light spectrum. On other aspects, absorption inthe visible spectrum is provided by photocatalysts comprising a blend ofTiO₂ and SiO₂ to create a 3.3 eV gap.

TABLE 3 Co-catalysts and absorption wavelengths Co-catalyst WavelengthGold (AU) visible Pt Ag titanium dioxide ceramic visible

Co-catalysts of the present disclosure may be provided in variousamounts relative to the catalyst. In general, co-catalysts can beprovided at levels of up to about 5%. In certain aspects, the amount ofco-catalyst is 5% or less, though mixtures of co-catalysts having acombined amount of up to 10% may be used in certain aspects. In certainaspects, up to 1.0% of the total mass of the catalyst may be aco-catalyst of the types described above. In some aspects, the totalamount of co-catalyst is up to 0.05%. In yet other aspects, theco-catalyst is provided at between 0.005 and 0.05%. In some aspects, theco-catalyst is provided at between 0.01 and 0.05%. In another aspect,the co-catalyst is provided at between 0.01% to 0.02%. In certainaspects, the co-catalyst is provided a less than 0.05% of the total massof the catalyst.

The catalysts of the present disclosure may further include one or moreadditives. In an aspect, an additive may be a hygroscopic additive. Notto be limited by theory, it is thought that the presence of ahydroscopic additive increases the local concentration of water on thephotocatalytic surface and thereby provide for non-hydrated purifiedhydrogen peroxide gas production at lower humidity levels and improvesthe efficiency of PGPG production at higher humidity levels. As providedherein, catalyst coatings having hygroscopic agents extend theefficiency of PHPG generating devices and extends the range of relativehumidities wherein the PHPG generative device operates efficiently andcan produce PHPG at a rate sufficient to establish a steady stateconcentration of PHPG of at least 0.005 ppm in a closed air volume of 10cubic meters. In certain aspects, the relative humidity can be as low as1%. In an aspect, the humidity of the ambient air is preferably aboveabout 1% relative humidity (RH). In certain aspects the relativehumidity can be from 1 to 99%. In other aspects, the humidity of the airflowing through the air permeable substrate is between 1% and 20% RH. Infurther aspects, the humidity of the air flowing through the airpermeable substrate is at or above 5%. In other aspects, the humidity ofthe ambient air may be between about 10% and about 99% RH. In otheraspects, the humidity of the ambient air may be between about 10% andabout 99% RH. In certain aspects, the humidity of the air flow is lessthan 80%. In an aspect, the humidity is between 10% and 80%. In yetother aspects, the relative humidity is between 30% and 60%. In anotheraspect, the humidity is between 35% and 40%. In some aspects, thehumidity of the air flowing through the air permeable substratestructure is between 56% and 59%.

In aspects according to the present disclosure, the hygroscopic additivemay be selected from the group consisting of sodium bicarbonate,potassium bicarbonate, sodium carbonate, potassium carbonate, magnesiumcarbonate, magnesium bicarbonate, sodium hydroxide, potassium hydroxide,magnesium hydroxide, zinc chloride, calcium chloride, magnesiumchloride, sodium phosphate, potassium phosphate, magnesium phosphate,carnallite (KMgCl₃.6(H₂O)), ferric ammonium citrate, nylon,acrylonitrile butadiene styrene (ABS), polycarbonate, cellulose,poly(methyl methacrylate), and combinations thereof.

In aspects according to the present disclosure, the hygroscopic additivemay be a salt. In certain aspects, a hygroscopic additive may be abicarbonate. In an aspect, the hygroscopic additive is sodiumbicarbonate. In an aspect, the hygroscopic additive is potassiumbicarbonate. In an aspect, the hygroscopic additive is magnesiumbicarbonate. In other aspects, a hygroscopic additive may be acarbonate. In an aspect, the hygroscopic carbonate is sodium carbonate,potassium carbonate, or magnesium carbonate. In some aspects, thehygroscopic additive may be a hydroxide. In certain aspects, thehygroscopic additive may be sodium hydroxide, potassium hydroxide, ormagnesium hydroxide. In some aspects, the hygroscopic additive may be achloride. In certain aspects the hygroscopic additive may be zincchloride, calcium chloride, or magnesium chloride. In yet other aspects,the hygroscopic additive may be a phosphate. In certain aspects, thehygroscopic phosphate may be sodium phosphate, potassium phosphate, ormagnesium phosphate. It is understood that one or more hygroscopiccompounds may be combined.

In general, additives can be provided at levels of up to about 5%. Incertain aspects, the amount of additive is 5% or less, though mixturesof additives having a combined amount of up to 10% may be used incertain aspects. In certain aspects, up to 1.0% of the total mass of thecatalyst may be an additives of the types described above. In someaspects, the total amount of additive is up to 0.05%. In yet otheraspects, the additive is provided at between 0.005 and 0.05%. In someaspects, the additive is provided at between 0.01 and 0.05%. In anotheraspect, the additive is provided at between 0.01% to 0.02%. In certainaspects, the additive is provided at less than 0.05% of the total massof the catalyst.

The present disclosure further provides for and includes a catalystsurface having a pH of 6.0 or greater. Not to be limited by theory, itis thought that the higher pH provides an improved source for oxidizablehydroxide ions during photocatalysis thereby increasing the productionof non-hydrated purified hydrogen peroxide gas. In an aspect, the pH ofthe catalyst surface is greater than pH 7.0. In another aspect, the pHof the surface is between 7.0 and 9.0. In an aspect, the pH of thecatalyst surface is between 7.0 and 8.5. In an aspect, the pH of thecatalyst surface is between 7.0 and 8.0. In an aspect, the pH of thecatalyst surface is between 7.0 and 7.5. In another aspect, the pH ofthe surface is between 7.5 and 9.0. In an aspect, the pH of the catalystsurface is between 7.5 and 8.5. In an aspect, the pH of the catalystsurface is between 7.5 and 8.0. In another aspect, the pH of the surfaceis between 8.0 and 9.0. In an aspect, the pH of the catalyst surface isbetween 8.0 and 8.5. In certain aspects, the pH of the surface is atleast 7.5. In certain aspects, the pH of the surface is at least 8.0.

Catalysts of the present disclosure, optionally including co-catalystsand additives may be prepared according to methods known in the art.Suitable co-catalysis and additives include silver nitrate, cerium oxideand zinc oxide. Additives are included to reduce, for example, bacterialgrowth and to prevent UV induced degradation of the catalyst and airpermeable substrate. The catalysts, co-catalysts and additives of thepresent disclosure may be applied to a mesh by a variety of methodsincluding, but not limited to, gel sol methods, painting, dipping, andpowder coating. In other aspects, the catalysts, co-catalysts andadditives of the present disclosure may be applied to a mesh by tollcoating, tape casting, ultrasonic spray, and web-based coating. Asprovided herein, the method of applying the catalysts, co-catalysts andadditives is suitable if it provides for, and includes, retaining themesh of the underlying air permeable substrate as recited above.

In an aspect, the catalyst mixture is applied to a mesh using a sol-gelmethod comprising the use of an alcoholic metal salt as the catalyticmaterial. In certain aspects, the metal salt is Ti(OR)₄. Application ofa catalyst mixture using the sol-gel method may further include organicand inorganic salts in the alcoholic solution to carry on hydrationreaction, thereby producing organic metal compounds in gel form. Thesol-gel methods may further include co-catalysts such as WO₃, SnO₂,Fe₂O₃, or ZnO. The gel solution may be applied by dipping the mesh intothe gel solution or painting the solution onto the air-permeablesubstrate structure. The thickness of the catalyst mixture applied tothe substrate may be controlled by controlling the dipping speed or byproviding one or more coats. After drying, the coated substrate is bakedand then sintered at high temperatures. In certain aspects, thecatalytic mixture may further include noble metals or transition metals.In some aspects, the catalyst mixture may further include noble metalssuch as Au, Pd, Pt, or Ag, and some transition metals such as MoO₃,Nb₂O₅, V₂O₅, CeO₂, or Cr₂O₃.

The present disclosure provides for and includes devices having a sourceof light capable of illuminating the air permeable substrate structurehaving a catalyst on its surface. Not to be limited by theory, uponillumination, the catalyst absorbs photons of the appropriate wavelengthand the energy is imparted to a valence band electron. The valence bandelectron is promoted to the conduction band creating an electron-hole orvalence band hole. In the absence of an adsorbed chemical species, thepromoted electron will decay and recombine with the valence band hole.Recombination is prevented when the valence band hole captures anelectron from an oxidizable species—preferentially molecular wateradsorbed to an active surface site on the photocatalyst. Concurrently, areducible species adsorbed on the catalyst surface—preferentiallymolecular oxygen—may capture a conduction band electron.

Light sources suitable for devices of the present disclosure includeboth wide and narrow spectrum emission sources. In certain aspects, thelight source may emit light in the ultraviolet (UV) spectrum. In otheraspects, the light source may emit light in the visible spectrum. In yetother embodiments, the light source may emit light in both the visibleand ultraviolet spectrums.

Suitable light sources according the present disclosure include, but arenot limited to, lasers, light emitting diodes (LED), incandescent lamps,arc lamps, standard fluorescent lamps, U.V. lamps, and combinationsthereof. In certain aspects, the light source is a light emitting diode.

The present disclosure provides for and includes illuminating anair-permeable substrate structure coated with a catalyst mixture usinglight of a suitable wavelength and intensity. As provided above,selection of a suitable illumination wavelength is determined by thecatalyst and may be modified by the presence of one or moreco-catalysts. In certain aspects, the light source provides ultravioletlight. In an aspect, the wavelength of the ultraviolet light is from 190nm to 410 nm. In some aspects, where the light source may provide lighthaving wavelengths of less than 190 nm, a suitable filter may be furtherprovided to the device to block light at wavelengths of 190 nm andbelow. More specifically, certain devices of the present disclosureexclude light having a wavelength at or below 187 nm.

One of ordinary skill in the art would recognize that the production ofozone would result in the reduction of PHPG gas to water and oxygen:O₃+H₂O₂⇄H₂O+2O₂Accordingly, prior art designs that produce ozone are incompatible withthe methods and devices of the present disclosure. As noted above,avoiding light at wavelengths below 190 nm for titanium dioxidecontaining catalysis greatly reduces or even eliminates ozone productionand results in higher rates of PHPG production.

In certain aspects, the device includes an ultraviolet light sourcecapable of illuminating a titanium dioxide containing catalyst mixturewith light from 190 nm to 410 nm and may further include a filter toblock light at wavelengths of 190 nm and below. In other aspects, thedevice includes both an ultraviolet light source providing illuminationof a catalyst mixture containing titanium dioxide and further includes aco-catalyst that extends the absorption band of photocatalysis into thevisible spectrum. In an aspect, the catalyst mixture may includetungsten trioxide, WO₃, that absorbs light in the visible spectrum. Inan aspect, the light source may include light from 190 nm to 460 nm.

In further aspects, the light source provides ultraviolet light having aspectrum of light of 190 nm to 460 nm wherein 70% of the power isprovided between 340 nm and 380 nm. In an aspect, at least 90% of theultraviolet light is emitted between 340 nm and 380 nm. In anotheraspect, 99% of the ultraviolet light is emitted between 350 nm and 370nm. In a further aspect, the ultraviolet light has a wavelength in theUVA range (315 nm to 400 nm). In some aspects, the light in the UVArange has a maximal intensity centered on or about 362 nm. In anotheraspect, the ultraviolet light has a wavelength in the UVA range and lessthan 1% in the UVB range (280 nm to 315 nm). In a further aspect, theultraviolet light has a wavelength in the UVA range and less than 0.1%in the UVB range. In yet a further aspect, the ultraviolet light has awavelength in the UVA range and less than 0.05% in the UVB range.

In aspects according to the present disclosure, a light source may havea power of 0.1 W to 150 W. In other aspects, the light source may be upto 150 W. In another aspect, the power may be at least 0.1 W. In anaspect, the light source has a power of at least 1 W. In a furtheraspect, the power may be greater than 2.5 W. In an aspect, the power maybe about 5 W. In an aspect, the power may be 20 W. In certain aspects,the power of the light source may be up to 100 W. In certain aspects,the power is less than 100 W to minimize the destruction of PHPGproduced. In other aspects, the power is between 1 W and 50 W. Incertain aspects, the power of the light source is between 40 and 50 W.

Devices of the present disclosure include light sources providing anintensity of at least 0.1 watts per square inch (W/in²) as measured atthe air permeable substrate surface. In some aspects, the light sourcehas an intensity of up to 150 W/in². In other aspects, the light sourceoutputs light having an intensity of between 0.1 W/in² to 10 W/in². Inan aspect, the intensity of the light illuminating the air permeablesubstrate is about 5 W/in². In certain aspects, the power at thesubstrate surface may be between 1 W/in² to 10 W/in². In another aspect,the intensity may be between 2 W/in² and 8 W/in². In an aspect, theintensity may be between 3 W/in² and 7 W/in². In yet another aspect, thepower may be between 4 W/in² and 6 W/in².

Devices of the present disclosure are distinguishable from devicesemploying photocatalysis to produce reactive species that are designedfor filtration. More specifically, devices of the present disclosure aredegraded by the presence of contaminants such as dust, pollen, bacteria,spores, and particles that can occlude the open spaces of a mesh of theair permeable substrate. Similarly, volatile organic compounds (VOCs)which can react with reactive species, including hydrogen peroxide,decrease the production of PHPG and the distribution of PHPG to a space.Notably, while VOCs can be effectively reduced in a space by PHPGproduced devices of the present disclosure, VOCs introduced into thedevice itself are preferably minimized or eliminated altogether.Accordingly, to maintain the efficiency of the devices and to maximizePHPG production, devices of the present disclosure may include one ormore filters. As will be noted, the selection of the filters may bedetermined by the application and the type of space to be treated usingPHPG. For example, a clean room in which air is already treated toeliminate dust, VOCs, and other contaminates could employ a devicehaving an enclosure, an air distribution mechanism, a light source, andan air permeable substrate having a catalyst on its surface withoutrequiring a prefilter. In contrast, a device for home use might requirea dust filter and might further require a carbon filter to absorb VOCs.In certain aspects, the inclusion of an additional filter provides forthe extended life of the air permeable catalyst coated substrates andprovides for extended production of PHPG.

Filters used to purify air unrelated to PHPG generation are dependent onthe air quality of the location in which the device is used. Inside anHVAC system with high quality air achieved by the filters of the HVACsystem, no filters may be necessary before the air flow passes throughthe air permeable substrate of the PHPG device itself. The same holdstrue for stand-alone devices operating in areas where there is high airquality. When necessary, filters are generally selected from those knownin the art that can achieve the filtration required with as littleimpedance of air flow necessary. Filters are further selected from thoseknown in the art so that the filter itself does not also not introduceparticulates or gasses into the airstream. Suitable filters that combinethe functions of removing particulates as well as gaseous contaminantsare known in the art. Filters require replacement regularly, with afrequency determined by the load placed upon the filter due to higherair quality (less frequent replacement) or lower air quality (morefrequent replacement).

In most applications three filtration concerns are applicable. Incertain applications, particulates or dust can foul the substrate matrixand the catalyst itself, so a particulate filter sufficient to the needsof the location may be used. In certain common aspects, a high air flow,pleated MERV 18 filter is employed. In other applications, volatileorganic hydrocarbons may require filtration and this may be accomplishedusing a number of different activated charcoal or carbon impregnatedfilters that are known in the art. In yet other applications, certaininorganic gasses such as nitrogen oxides need to be removed byfiltration. To remove nitrogen oxides, a zeolite filter is usuallyemployed. In some aspects, the PHPG device includes impregnated zeolitefilters that are capable of removing volatile organic hydrocarbons andnitrogen oxides in a single, combined material and stage. Suitablefilters are known in the art that can remove particles of various sizesthat would otherwise block the air permeable substrate or contaminateand inactivate the catalytic surface.

In aspects of the present disclosure, devices may further include one ormore filters designed to remove contaminants selected from nitrogenoxides (NOx), sulfur oxides (SOx), volatile organic compounds, dust,bacteria, pollen, spores, and particles. In certain aspects, the deviceincludes one or more filters selected from an organic vapor filter, aparticulate filter, a high efficiency filter, a hydrophobic filter, anactivated charcoal filter, or a combination thereof.

In certain aspects, pre-filters remove volatile organic compounds, NOx,and SOx. In some aspects, the filters remove aldehydes such asformaldehyde or acetaldehyde. In other aspects, the filters remove VOCsincluding toluene, propanol, and butene. In yet other aspects,pre-filters remove the mono-nitrogen oxides NO and NO₂ (e.g., NOx). Inother aspects, pre-filters remove sulfur and oxygen containing compoundsknown as SOx. SOx compounds removed by filters of the present disclosureinclude SO, SO₂, SO₃, S₇O₂, S₆O₂, S₂O₂, or combinations thereof.Prefilters of the present disclosure may be employed to remove anycombination of VOCs, NOx, and SOx.

In certain aspects, the devices include a filter comprising amicroporous aluminosilicate mineral. In an aspect, a filter of thepresent device may be a zeolite filter. In an aspect, the zeolite may beanalcime, chabazite, clinoptilolite, heulandite, natrolite, phillipsite,or stilbite. In certain aspects, the zeolite may be a synthetic zeolite.In an aspect, the device includes a zeolite filter for the removal ofNOx, SOx, or both. Suitable filters are known in the art.

In other aspects, the devices include a filter comprising a particulatefilter. In certain aspects, the particulate filter is a 3 m ultraallergan filter. A suitable example of a particle filter can be obtainedfrom Air Filters, Inc, which provides Astro-cell mini-pleat filters. Oneof ordinary skill in the art would be able to select filters thatprovide suitable air flow levels and resistance to air flow to providefor a sufficient air flow through the air permeable substrate as recitedabove.

In yet other aspects, suitable filters for devices of the presentdisclosure include carbon filters, charcoal filters, or activated carbonfilters. In some aspects, the filter is a GAC (granular activatedcarbon) carbon filter. In an aspect, the GAC is a filter prepared fromcoconut shells. In an aspect, the filter is a powdered activated carbon(R 1) (PAC). In another aspect, the filter is an extruded activatedcarbon (EAC) filter. In an aspect, the filter may be a bead activatedcarbon (BAC) filter. In an aspect, the filter may be an impregnatedcarbon filter. In certain aspects, an impregnated carbon filter isincluded in a device to remove hydrogen sulfides (H₂S) and thiols.Suitable impregnated carbon filters are known in the art.

Air filtration in devices according to the present disclosure providefor air flows across the air permeable substrate layer having low levelsof contaminants and photocatalysis inhibitors.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

Various embodiments and aspects of the present invention as delineatedhereinabove and as claimed in the claims section below find experimentalsupport in the following Examples. The following Examples are presentedfor the purposes of illustration and should not be construed aslimitations.

EXAMPLES Example 1: Measurements of PHPG, Ozone, VOC's, Temperature, andHumidity

All PHPG concentration readings take place with Draeger products. A PacIII, Polytron 7000 or Draeger Tube is utilized in all tests, generallyaccording to manufacturer's instructions. The Polytron displays adigital reading when air is drawn through the mesh sensor. Mostcommonly, Draeger Tubes are used after clipping on both ends andplacement in a ACCURO™ Pump. Per manufacturer instructions, the tubesare pumped 100 times and the level of PHPG determined by observing thecolor change in the crystals. The PAC III has proved to be generallyless effective in measuring very low levels of PHPG.

Measurements for ozone, VOC's, temperature, and humidity were allaccomplished using standard devices. Draeger tubes, designed to detecthydrogen peroxide concentrations as low as 0.10 ppm after drawing 2000cubic centimeters of air, are found to provide readings of lowerconcentrations accurate within 0.005 ppm, as larger volumes are drawn bya calibrated pump—for example, a Draeger tube that indicated 0.10 ppmafter drawing 4000 cubic centimeters measure an approximate PHPGconcentration of 0.05 ppm, and a Draeger tube that indicated 0.10 ppmafter drawing 6000 cubic centimeters, measured an approximate PHPGconcentration of 0.033 ppm.

Example 2: PHPG Devices Testing Air Permeable Substrates

A PHPG generating device 20 as illustrated in FIGS. 2A to 2B comprisingan enclosure 205, an air permeable substrate 201, an air distributionmechanism 203 and a light source 203 is used for testing. The airpermeable substrates 201 are prepared by dip coating a polyester mesh ina 10 to 35% slurry of the anatase form TiO₂ in water and allowed to airdry. To prevent clogging of the open holes of the mesh, air is blownthrough the air permeable substrate. The air distribution mechanism isset on its highest setting and provides an airflow of about 115 cubicfeet per minute. The humidity of the room is maintained at approximately55%. The PHPG generating device is allowed to operate in a 140 squarefoot closed room with 8 foot ceilings for 1 hour and then the steadystate level of PHPG is determined. Absent the continued operation of thePHPG generating device, the PHPG dissipates and is undetectable withinabout 5 minutes. Ozone is not detected in any of the tests.

Example 3: Effect of Mesh Variation on PHPG Production

The effects of mesh variation on PHPG production is performed byreplacing the TiO₂ coated air permeable substrate 201 as provided inTable 4 and testing as described in Example 2.

TABLE 4 Comparison of Air Permeable Substrates Thread Thread HoleStrands Thick- Hole Open Thickness Size Per ness size Strands Area PHPG(inches) (inches) Inch (μm) (μm) per cm % (ppm) 0.0019 0.001 460 48 25181 21 0.1 0.0024 0.002 280 61 51 110 30 0.4 0.0045 0.004 140 114 102 5537 0.3 0.0051 0.006 109 130 152 43 45 0.3 0.006 0.008 80 152 203 31 410.6 0.013 0.012 50 330 305 20 37 n/d 0.016 0.032 24 406 813 9 58 n/d n/d= not detected

Example 4: Effect of Angle of Incidence on PHPG Production

The device according to Example 2 is modified by attaching a 10 inchaluminum adaptor as a shroud to the top of the device that allows forrotation of the air permeable substrate 201. An air permeable substratehaving 152 micron threads and an open area of 41% is placed in thedevice. The initial steady state level of PHPG, measured having theairflow at 90°, is 0.7 ppm. The air permeable substrate 201 is rotatedwithin the shroud in 2° increments and the steady state level of PHPGmeasured until the polytron no longer detects hydrogen peroxide.Production of PHPG is maintained from about 90° to about 68° (e.g., 22°off perpendicular). Beginning at about 68°, PHPG levels decreasessteadily from 68° degrees to about 14° at approximately 0.1 ppm per 10°.No PHPG production is detected when the incident angle of the airflowwas below 14°.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications, and variations that fall within the spirit and broadscope of the appended claims.

All publications, patents, and patent applications mentioned in thisspecification are herein incorporated in their entirety by referenceinto the specification, to the same extent as if each individualpublication, patent, or patent application was specifically andindividually indicated to be incorporated herein by reference. Inaddition, citation or identification of any reference in thisapplication shall not be construed as an admission that such referenceis available as prior art to the present invention. To the extent thatsection headings are used, they should not be construed as necessarilylimiting.

The invention claimed is:
 1. A device for producing non-hydratedpurified hydrogen peroxide gas (PHPG) comprising: a. an enclosure; b. anair distribution mechanism providing an airflow; c. an air-permeablesubstrate structure that is a mesh having a percentage of open areabetween 10% and 60%, said mesh having a catalyst on its surface; d. asource of light; and wherein said airflow is through said air-permeablesubstrate structure; and said device produces PHPG and directs it out ofsaid enclosure when in operation.
 2. The device of claim 1, wherein saidcatalyst comprises titanium dioxide and said source of light is a sourceof ultraviolet light.
 3. The device of claim 1, wherein said catalystcomprises tungsten trioxide or a mixture of titanium dioxide andtungsten trioxide and said source of light is visible light with anenergy of at least 2.85 electron volts (eV).
 4. The device of claim 1,wherein said catalyst comprises titanium dioxide.
 5. The device of claim1, wherein said catalyst comprises tungsten trioxide or a mixture oftitanium dioxide and tungsten trioxide.
 6. The device of claim 1,wherein the thickness of said catalyst on the surface of said airpermeable substrate structure is between 250 nm and 750 nm thick.
 7. Adevice for producing non-hydrated purified hydrogen peroxide gas (PHPG)when installed into a heating, ventilating, and air conditioning (HVAC)system comprising: a. an air-permeable substrate structure that is amesh having a percentage of open area between 10% and 60%, said meshhaving a catalyst on its surface; and b. a source of light; wherein airflows from the HVAC system through said air-permeable substratestructure and said device produces PHPG and directs it away from saidair-permeable substrate structure having a catalyst on its surface whenin operation and into a heated, ventilated and air conditioned space. 8.The device of claim 7, wherein said catalyst comprises titanium dioxideand said source of light is a source of ultraviolet light.
 9. The deviceof claim 7, wherein said catalyst comprises tungsten trioxide or amixture of titanium dioxide and tungsten trioxide and said source oflight is visible light with an energy of at least 2.85 eV.
 10. Thedevice of claim 7, wherein said HVAC system further comprises one ormore filters to remove one or more contaminants from said airflow priorto flowing through said air-permeable substrate structure selected fromthe group consisting of nitrogen oxide (NOx), sulfur oxide (SOx),volatile organic molecules (VOM), household dust, pollen, dust-mitedebris, mold spores, pet dander, smoke, smog, and bacteria.
 11. Thedevice of claim 7, wherein the thickness of said catalyst on its surfacethat is between 5 nm and 750 nm thick.